Mara Desso

Principle(s) Illustrated

1. Nyctinastic movement.

2. Adaptations to environment

3. Turgor pressure

Standards

Questioning Script

Prior knowledge & experience:

Students likely already have heard of the venus fly trap, which is a plant that can move to consume prey. They also probably do not associate plants with movement from past experiences.

Root question:

Why does the mimosa plant move when touched?

How does the mimosa plant move when touched?

Target response:

Why does the mimosa plant move when touched?

The plant likely moves for two reasons. First, if an insect lands on the plant to eat it and the plant moves, the insect will likely be scared away or fall off the plant and move onto a plant with less defense. Second, at night, when the leaves close up, it may prevent water loss.

How does the mimosa plant move when touched?

When stimulated, either by absence of light (night time) or touch, the plant moves its leaves through altering the turgor pressure at the base of the leaves. The change in turgor pressure is due to the movement of potassium K+ ions out of the plant cells. This changes osmotic pressure at the base of the leaf as water also moves out of the plant cells and causes the collapse of the leaves inwards.

Common Misconceptions:

Students may think that the plant has a central nervous system. You can have a discussion with students about the similarities between the release of K+ during the plant movement and how our nerve cells send signals using Na+/ K+ ion movement. This will help them realize that this is a similar but very different process from our own nervous system.

Photographs and Movies

Mimosa Picture

Mimosa responding to touch

References

UCC The Sensitive Plant

NCBI Mimosa pudica L. (Laajvanti): An overview